[v11] Verify Fisheye: cube-map and Object3D render root on WebGPU

What it does

src/core/Portal/Fisheye/Fisheye.tsx:95-97 renders a sphere with an orthographic camera, after the main render:

useFrame(
  () => {
    if (renderPriority) gl.render(sphere.current, orthoC)
  },
  ...
)

The component builds a cube map of the scene and projects it onto that sphere, so there is a CubeCamera-shaped render path behind this as well as the visible gl.render.

What to check

• gl.render(sphere.current, orthoC) takes an Object3D as the "scene" argument. Both renderers accept that, but confirm the WebGPU Renderer handles a non-Scene root the same way — particularly around background, environment and fog handling, which _renderScene reads off the scene object.
• The cube-map update path. Fisheye depends on cube rendering, which is the same area that broke the /webgpu entry in #2764 (WebGLCubeRenderTarget is not exported from three/webgpu). Worth confirming what it is actually constructing under the WebGPU build.
• state.gl vs state.renderer — deprecated accessor, warns every frame.

Shared context (identical across all seven)

These components are classified agnostic — they live in core/, so they are assumed to work on both renderers. That assumption held for 104 of the 106 agnostic components when swept: 73 never touch the renderer at all, and 31 touch only members both renderers have. These seven are different: they drive their own render calls, and that is where semantics diverge even when the API surface matches. See #2818.

setRenderTarget(renderTarget, activeCubeFace = 0, activeMipmapLevel = 0) has an identical signature on both (Renderer.js:2578 vs WebGLRenderer.js:2890), so that part is fine.

render() is where they differ — three/src/renderers/common/Renderer.js:1362:

render( scene, camera ) {
  if ( this._initialized === false ) {
    throw new Error( 'THREE.Renderer: .render() called before the backend is initialized. Use "await renderer.init();" before rendering.' );
  }
  this._renderScene( scene, camera );
}

WebGL has no such gate. A render() that happens before the backend is ready throws on WebGPU and silently works on WebGL.

This is the class of bug that produced #2809: Preload calls gl.compile(), which on WebGPU is a getter aliasing compileAsync — same name, returns an unawaited promise, so preloading never happens. Grep cannot find these; they need reading.

Acceptance

Read the component against the WebGPU Renderer implementation and either confirm it is correct or fix it and say what was wrong. A story exercising the render path on WebGPU is the evidence — note Setup sets frameloop: 'never' under test, so useFrame does not run there and a green story proves nothing about this.